Find the period and the amplitude of the periodic function

Question

y=3cos 4x

Answer 1

when does 4 x = 2 pi , a full circle ?

x = 2 pi/4 = pi/2

the single amplitude is given, 3

Answer 2

for y = a cos(kx)
period = 2pi/k
amplitude = a

Answer 3

Answer is c
Period= 1/2pi; range:-3<y<3;amplitude=3